Summary: Although no epidemiological evidence has yet implicated blood or blood products in the spread of any human transmissible spongiform encephalopathy (TSE), animals experimentally infected with the agents of scrapie and two variants of Creutzfeldt-Jakob disease (CJD) were consistently found to have infectivity in blood during both the asymptomatic incubation period and overt illness, prompting precautionary recommendations by the FDA to defer donors at increased risk of TSEs. Almost all experimental studies of TSE infectivity have involved animals infected by direct intracerebral injection or, less often, by the intravenous route. Naturally acquired TSEs, however, are thought to result from dietary exposure to contaminated tissues or, perhaps, to exposure through cutaneous or mucosal lesions. We propose to infect scrapie-susceptible rodents (mice and hamsters) to infection by the oral route and by subcutaneous inoculation of small amounts of infectious scrapie agent, and then to follow the appearance of infectivity and of the abnormal protease-resistant "prion" protein (PrP-res) that generally accumulates in infected tissues when infectivity reaches high levels. We will assay for infectivity in various blood fractions (red cells, nucleated cells, platelets and plasma), separated lymphoid cells from nodes, spleen and bone marrow, neural tissues and from other solid organs (lung, liver, kidney, intestines) by intracerebral inoculations of rodents. PrP-res will be assayed using immunhistochemistry, Western immunoblot and ELISA. Each tissue will be collected from groups of three or more rodents of each species infected by each of the two routes. We anticipate that groups animals will be examined weekly for eight weeks and then monthly for ten additional months or until all surviving animals are ill. This project will be conducted jointly by investigators and support staff in DETTD's Laboratory of Bacterial, Parasitic and Unconventional Agents and in the Division of Hematology, Laboratory of Cellular Hematology, OBRR (J. Vostal and co-workers) and supported by the Division of Veterinary Services (P. Snoy). During the past fiscal year, a fellow and a technician were recruited to begin this project, renovations to a new laboratory suite were undertaken, and necessary equipment for histopathological and immunhistochemical examinations of animal tissues was procured. Preliminary studies with archived tissues from rodents with scrapie have begun.